1. Field of the Invention
The present invention relates generally to the metallization of polymers and more specifically to the metallization of carbonyl-containing polymers.
2. Description of the Prior Art
Because of the excellent physical and chemical properties of carbonyl-containing polymers such as poly(ethylene terephthalate) (i.e., PET), metallization (selective or otherwise) has been an object of keen interest to manufacturing. The major problem associated with the process has been achieving sufficient adhesion between the film and the metal to minimize delamination. Treatments usually involve immersion of the film in acidic or basic baths for varying amounts of time followed by one of several electroless plating processes using complex solution chemistry and sensitive balancing of electromotive force and weak metal complexation in solution. The pretreatment is believed to result in the breaking of carbonyl bonds yielding reactive carboxyl and hydroxyl groups.
Other techniques for applying metal to carbonyl-containing films such as PET involve spraying special adhesives directly on the film prior to electroless deposition and also glow discharge pretreatment followed by chemical vapor deposition.
Selective metallization has been achieved in the prior art using the general techniques described above, coupled additionally with the poisoning of desired areas to the metallization process, for example by the incorporation of impurities by various means. These prior art techniques are complex and require the use of various extraneous reagents.
Specifically, a patent by Aviram et al. (U.S. Pat. No. 4,440,801) describes the selective metalization of semicrystalline PET using high intensity, short wavelength ultra-violet laser irradiation through a lithographic mask, followed by chemical treatment in an ammonia bath, followed by electroless deposition of metal using standard techniques. Only in those areas exposed to the UV light was metal deposited from the electroless plating bath.
Rubner and Cukor (U.S. Pat. No. 4,486,463) describe a method for selective metallization of poly(phenylenesulfide)(PPS). Practice of their technique requires irradiation of amorphous PPS through a lithographic mask with an infra-red light source, chemical treatment, doping of amorphous regions of the polymer with a metallization poison, followed by metalliztion of the crystalline PPS using conventional electroless techniques.
Another technique for electroless deposition of metal onto a polymer substrate is described by Blum et al (U.S. Pat. No. 4,451,503 wherein a high intensity, short wavelength U.V. source is used to decompose metal carbonyl compounds into the zero valent metal state which then condense onto a polymer substrate lying in close juxtaposition. Selectivity of the metallization process occurs when the exciting light is scanned in a particular pattern.
Brown et al. (J. Appl. Poly. Sci. 35, 1988, 279-297.) report a method for depositing aluminum on PET with very strong metalpolymer adhesion. In this process the polymer is first subjected to the radiative effects of a glow discharge, and then metal vapor deposited to a thickness of tens of nanometers.
Warshawsky and Upson (Polymer, 30, 1989, 972-973.) describe a technique for the electroless deposition of metal on polymer surfaces whereby the polymer is activated by its soaking in a palladium catalyst solution, the reduction of the catalyst with one of several suggested agents, followed by the immersion of the polymer into an electroless plating bath.